The present invention relates to methods of growing high-quality CdTe-based materials at high rates by physical vapor deposition. CdTe-based single crystals are popular for infrared, x-ray, and gamma-ray detectors, as well as applications such as night image cameras, radiation monitors, and medical equipment. Related art methods to grow CdTe-based single crystals include the Bridgman technique and the traveler heating methods (THM). In these methods, large quantities of bulk CdTe material are melted in furnaces at very high temperatures and slowly cooled to form large single crystals over the course of days. These methods are very expensive and time-consuming.
Another related art approach to grow CdTe-based single crystals is molecular beam epitaxy (MBE). In this technique, CdTe is evaporated in ultrahigh vacuum and made incident onto a substrate target held at a temperature between about 150° C. and about 300° C. With this technique, single crystals typically grow at a rate of about 1 μm per hour. To grow a 70-μm film requires 3 days of equipment time. MBE equipment is very expensive, maintenance requirements are frequent, and operation is costly.
On the other hand, close-spaced sublimation (CSS) and vapor transport deposition (VTD), performed under moderate vacuum conditions of approximately 10 Torr, deposit CdTe at rates 100-1000 times faster than MBE. However, CdTe-based materials grown by these related art methods to date have been polycrystalline with small grains having a grain size that is roughly on the order of the film thickness, or about a micron or two in typical thin films. The grain boundaries are defective and reduce performance, but the low cost and fast throughput are advantageous for photovoltaic applications. Accordingly, it would be advantageous to provide a low-cost method of growing single-crystal or large-grain polycrystalline CdTe-based materials at fast growth rates.